At present, Dense Wavelength Division Multiplexing (DWDM) devices have been widely applied in the backbone networks and the local and metro core networks; the networking topology of the DWDM devices has transited from the simple point-to-point to the ring network and the two-ring intersection, and is finally applied in a mesh network. The service type has transited from a Time Division Multiplexing (TDM) service-based circuit switching service to an IP-based data service. Because of the uncertainty of the service development and the increase of difficulties in preliminary estimation, the devices are required to be intelligent, and required to rapidly and flexibly realize the service scheduling functions, so as to be adapted for the changes of the networking and service distribution when the network topologies and the service distribution have changed.
Similar to the Synchronous Digital Hierarchy (SDH) devices which enable the switching and scheduling for VC-4, the intelligence of the networks requires the DWDM devices to provide the reconfigurable functions based on the wavelength, i.e., wavelength Reconfigurable Optical Add Drop Multiplexing (ROADM), which can flexibly enable the add and drop multiplexing function of the wavelength and implement remote configuration. The ROADM can realize any point-to-point connection without manual deployment, and can realize the adding, dropping and straight-through configuration of the single wavelength. The ROADM technology can increase the flexibility of the Wavelength Division Multiplexing (WDM) network, make the network operators remotely and dynamically control the wavelength transmission path, and effectively reduce the operation and maintenance cost of the operators. Meanwhile, with the development of the network scale and the diversity of the service types, a multidirectional intelligent ROADM system which can realize the service broadcast function needs to be provided.
FIG. 1 shows a diagram of an existing ROADM device. The device comprises three parts which are a circuit direction, a dropping unit and an adding unit. In particular, after the optical signals, which are transmitted through the optical fibres from the direction 1 to the direction X respectively, enter into a dispersion compensation module in the direction (the module is selected according to the dispersion and the dispersion tolerance of the system) to be implemented with dispersion compensation, the optical signals then enter into an Optical Preamplifier (OPA) in the corresponding direction to be amplified to make up for the line loss. And then they enter into the couplers of the circuit direction in the corresponding direction to broadcast the optical signals in the direction to the Wavelength Selective Switch (WSS) and the dropping unit in each circuit direction in the form of broadcast. The WSS in the circuit direction of the direction broadcasts the inputted signals which are inputted to the direction from each direction, and multiplex it with selected wavelength signals from the signals inputted by the adding unit. And then, the WSS outputs the wavelength signals which are implemented with the optical multiplexing to the dispersion compensation module (the module is selected according to the dispersion and dispersion tolerance of the system), and then to the circuit optical fibre after the signals are amplified by the Optical Booster Amplifier (OBA). The wavelength scheduling among the X circuit direction can be realized through the matching of the units, and the wavelength scheduling can be realized through remotely controlling the WSS by the network manager of the devices.
The dropping unit in FIG. 1 consists of couplers, WSSes, Optical Amplifiers (OAs), tunable filters and receivers (RXes), wherein the optical signals in the direction 1˜X which are broadcasted and dropped through the coupler in the circuit direction are distributed into multiple groups through power allocation by the coupler of the dropping unit (for example, the broadcasted optical signals can be distributed into 2 groups by adopting 1×2 couplers, and can be distributed into 4 groups by adopting 1×4 couplers, and so on). Each group is outputted after the WSS selects the wavelength signals which need to be dropped from the optical signals inputted in each direction to perform optical multiplexing, and is outputted to the tunable filter to select the dropping wavelength after being amplified by the OA. And it is received by the RX, so as to realize the directionless and colorless dropping functions. But each group cannot have the same wavelength dropping. The same wavelength can be divided into multiple groups of droppings by the couplers. The tunable filter can be realized by the WSS. And the reconfiguration of the dropping wavelength can be realized by the network manager of the devices through remotely controlling the WSS and the tunable filter.
The adding unit in FIG. 1 consists of WSSes, couplers 1, OAs, couplers 2 and transmitters (TX), wherein each group of the optical signals transmitted by the TX are outputted to the coupler 2 after optical multiplexing by the coupler 1 of the group and then being amplified by the OA. The coupler 2 outputs the multiplexed optical signals to the WSS in each direction in the form of broadcast, and the WSS in each direction outputs each group of the optical signals to the WSS in the circuit direction in the corresponding direction after selectively implementing optical multiplexing for the optical signals. The directionless and colorless dropping functions can be realized when the TX is the one with tunable wavelengths. But each group cannot have the same wavelength adding, the same wavelength can be divided into multiple groups, and can be realized by the WSS through selectively implementing optical multiplexing for each group of signals. The reconfiguration of the adding wavelength can be realized by the network manager of the devices through remotely controlling the WSS and the TX with tunable wavelengths.
However, the related art only can realize part of the colorless, i.e., the dropping wavelength under each wavelength selection and the allocation unit cannot be the same, and the adding wavelength under each optical multiplexing and the allocation unit cannot be the same. Furthermore, as the adjustable optical filter array is immature, although the WSS is adopted to realize the reconfigurable dropping at present, the WSS apparatus is expensive. The WSS apparatus with more than 9 ports is immature, and multiple WSSes are needed when realizing the adding and dropping with more wavelengths. Thus the ROADM device has a high cost and a large size.